NOT APPLICABLE
NOT APPLICABLE
The present invention generally relates to apparatuses used to affect a thermal process on semiconductor (silicon) wafers by heating the wafer via convection heating. The wafers are subjected to a programmed temperature profile. The heat transfer mechanism is convection heat transfer via a heated gas, which may be air, nitrogen, or any specific transfer gas suited to the intended process.
Semiconductor wafer fabrication requires thermal process steps where the wafer is heated to specific temperatures and maintained at said temperatures for specific times. Typical processes require a series of successive temperatures to be achieved for specific time intervals.
Additionally, circuit boards require so-called re-melting of solder to finish connection of placed components to conductive channels (solder pads) on the circuit boards. In such remelting, precise temperature control is paramount. Temperature must be sufficient to permit the re-melting without component damage due to undue heating.
The specific process step and temperature to be attained determines which heat transfer method is best suited. In what follows, I will concentrate on wafer treatment. The reader will understand that circuit board treatment is also a use for the technology disclosed here.
Conventional (existing) wafer convection thermal processes are based on either batch or in-line configurations. This invention provides an alternate means for processing wafers, one-at-a-time, in a process chamber that provides better uniformity in heating and more flexibility in process conditions than can be achieved in either the batch or in-line processes.
In the batch process, a number of wafers are held in a process chamber, and subjected to flow of heated transfer gas. Because each wafer is not subjected to exactly the same environment, the process results and conditions vary from wafer to wafer. The temperature profile is achieved by varying the temperature of the convection gas stream.
In the in-line configuration, wafers are placed either directly on a conveyor or on a carrier attached to the conveyor designed to hold wafers. The conveyor moves the wafers through a sequence of temperature zones, each which is held at a fixed temperature. The temperature profile is achieved by passing the wafer through a sequence of oven zones, each being at a temperature step required in the process. Each wafer sees thermal stresses to the leading edge transitioning to a new temperature zone while the trailing edge of the wafer is still at the previous zone temperature.
I am unaware of convection heating being utilized to treat single wafers.
A thermal processing chamber configured to enclose and heat treat a single electronic substrate at an exposed surface, such as a wafer or electronic circuit board being re-melted, includes an enclosed gas tight and particle free heat insulated chamber. An electronic substrate support is placed within the enclosed gas tight and particle free heat insulated chamber. A convection gas inlet distribution manifold adjustable in spatial relation towards and away from the surface to be treated provides a flow of heated gas over and onto the exposed surface of the electronic substrate to be treated. A heated convection gas outlet is placed below the electronic substrate for the collection of heated gas after flowing over, around and below the exposed surface of the electronic substrate to be treated. A door is movable between and open and closed position. The door opens a path to move the electronic substrate into and out of the chamber to and from the electronic substrate support in an open position. The door has a gas-tight seal with respect to the chamber when in the closed position. A heater having an inlet for receiving gas, and an outlet for discharging heated gas provides heated gas for the convection treatment. A heat exchanger receives gas from the convection gas outlet and discharges gas to the heater inlet to enable heat recovery from the gas discharged from the convention gas outlet and to simultaneously enable precise temperature control. Provision is made for disposing individual ovens in juxtaposition to enable multiple substrates to be processed simultaneously.
This invention applies to wafer and circuit board processes where heating by convection is the primary heat transfer means, although some small percentage of the heat transfer may be via radiation or conduction.
The present invention provides a practical means to achieve single-wafer thermal convection processing with high process uniformity for a wide variety of process types, while achieving high through-put normally not achievable in a single-wafer processing configurations. Also, the form of the invention is well suited to utilize conventional wafer handling means such as 3-axis SCARA type robots with both vacuum and edge-grip end-effectors. By using standard wafer handling components, costs are reduced, reliability is improved, and contamination effects are lowered when compared to other handling means.
The invention consists of a single-wafer process chamber design, which is modular in nature, enabling clustering of multiple process chambers in both vertical and radial arrangements. The modular nature of the process chamber greatly simplifies connections to the transfer gas inlets and outlets, as well as power connections for heaters and control connections. Also important, its size allows for the close proximity of chambers, allowing a single robot to access multiple chambers from a single fixed robot location. In this clustered configuration, multiple single-wafer chambers can be run in parallel, thereby achieving throughput equal to or greater than batch or in-line processes.
Also significant, the small size and flexible wafer handling allows the thermal process system to be closely coupled to the upstream wafer process system which applies the coating which drives the need for the subsequent thermal process step. This enables a closely controlled time interval from the time when the coating is first applied to when the coating is cured, fixed, or re-flowed. Also significant is that with application and cure (or bake, or re-flow) combined, the wafers enter and leave the over-all system is a stable state, with no time dependencies or special handling required.
The modular process chamber has a side-opening door for placement of the wafer by an external robot, and lift pins or edge supports to hold the wafer in place. The process chamber is thermally insulated, and has an entry gas manifold in the chamber top, and an exit gas manifold in the chamber bottom. The design of the gas manifolds for the inlet gas flow is very important to direct the gas flow onto the wafer surface to achieve the uniformity required. The exit gas manifold design is equally important so the exiting gas is uniformly distributed about the chamber bottom and the backside of the wafer.
To achieve the desired temperature control, a controller measures the exit gas temperature, and heat input is adjusted to the inlet gas stream. Also, the fan speed is variable, allowing for the optimum gas flow velocity to be achieved for each stage of the wafer recipe profile. Higher flows are used to ramp temperatures, and lower flows to maintain a fixed temperature. The showerhead distance from the wafer is adjustable, as well as the sizes and locations of the individual holes (nozzles).
The major benefits that this invention brings to this technology area is that each wafer sees exactly the same process conditions ensuring good uniformity between wafers. The single wafer chamber design also allows many parameters to be adjusted to match the process requirements for each wafer: the convection gas flow velocity, distribution path, and distance from wafer face of the incoming heated gas showerhead; this assures uniformity on a single wafer. This level of tuning to each wafer is not possible with existing thermal convection systems such as batch and in-line systems. Also, each wafer can see a unique recipe compared to all other wafers; in existing batch and conveyor systems all of the wafers must have the same recipe. The fact that each wafer can have a unique recipe speeds development time when a great number of recipe parameters must be varied in an effort to fine tune a process recipe.
The invention includes features which make it energy efficient: The heat exchanger for reheat of the incoming gas recovers 50% of the thermal input energy. The variable speed fan allows for minimal airflow and energy input whenever steady-state conditions are required.
The invention allows for advantages in uniformity for all thermal processes. In addition, the single-wafer nature of the invention offers significant advantages to process steps where a previous process step applied a substance to the wafer surface, which then must be dried, stabilized, or re-flowed within a specific time limit.